Double-acting hydraulic pump and air motor therefor

ABSTRACT

A hydraulic pump and double-acting air motor therefor including means for controlling the inlet and exhaust of air to and from the opposite sides of the piston in the air cylinder. A pilot valve operated by the air piston controls one operating valve for the cylinder and a pilot relay valve. The pilot relay valve controls another operating valve which is in reverse phase with respect to the first-operating valve. The piston-operated pilot valve has a snap action feature so that the pilot valve, the pilot relay valve and the operating valves all reverse condition abruptly with a minimum dwell to provide a smoother power transmission. Also a muffler which inhibits ice formation is operatively associated with the operating valves for muffling the noise of the air being exhausted from the air cylinder through the operating valves with minimal accumulation of ice.

United States Patent Rosen et a1.

[54] DOUBLE-ACTING HYDRAULIC P AND AIR MOTOR THEREFOR [72] Inventors: Samuel R. Rosen, Lorain; Alvln A. Rood, Westlake; Donald R. Schorl, Amherst, all of Ohio [73] Assignee: Nordson Corporation, Amherst, Ohio [22] Filed: Mar. 211, 1969 [21] Appl. No.: 809,235

3,218,935 11/1965 York at al ..91/346 Primary Examiner-Paul L. Maslouslcy Attorney-Bosworth, Sessions, l-lenstrom and Cain [57] ABSTRACT A hydraulic pump and double-acting air motor therefor including means for controlling the inlet and exhaust of air to and from the opposite sides of the piston in the air cylinder. A pilot valve operated by the air piston controls one operating valve for the cylinder and a pilot relay valve. The pilot relay valve controls another operating valve which is in reverse phase with respect to the first-operating valve. The pistonoperated pilot valve has a snap action feature so that the pilot valve, the pilot relay valve and the operating valves all reverse condition abruptly with a minimum dwell to provide a smoother power transmission. Also a muffler which inhibits ice formation is operatively associated with the operating valves for muffling the noise of the air being exhausted from the air cylinder through the operating valves with minimal accumulation of ice.

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ATTORNEYS HYDRAULIC PUMP IN UPSTROKE FIG. l8

BACKGROUND OF THE INVENTION This invention relates to pneumatic motors and double-acting liquid pumps, and especially to systems for controlling single cylinder, double-acting air motors with reciprocating pistons used to drive associated equipment such as a pump piston. One aspect of the invention relates to the control system for alternately supplying air under pressure to one side of the cylinder while exhausting air from the opposite side and vice versa.

The invention has particular utility in connection with double-acting liquid pumps used to pump liquid paint to a spray gun.

A particular problem in the art to which our invention pertains is that of admitting air to and exhausting air from a pneumatic motor, particularly a double-acting motor, with a minimum resistance to flow of air to and from the cylinder of the motor and with leakproof reversal of the flow of air at the end of each stroke of the piston to maintain as nearly as practicable a continuous, true and reversing thrust output from the piston without deleterious diminution as its speed and load is increased to a reasonably desired maximum. A particular problem which has been solved by our invention is the inhibition of the formation of ice in and around the locations where air is exhausted from the cylinders and where the presence of water vapor in the air and abrupt drop in pressure at the exhaust ports encourages the formation of ice.

While the invention will be described in connection with air motors and particularly the problems deriving from the employment of moisture laden air, air is illustrative of all compressible fluids which may be employed in fluid motors controlled by our system advantageously.

As indicated above, the invention has particular utility in connection with the control of air motors for operating pumps for pumping paint or hot paint in the socalled hot airless method of spray painting. This method is disclosed and discussed in detail in US. Pat. Nos. 2,754,228 and 2,763,575 of James A. Bede. in this method the paint, whether hot or cold is projected from a small orifice nozzle under high pressure and the continuity of an even pressure is most desirable to obtain the best results.

Such air motors have in the past conventionally been operated by means of a four-way air valve such as that disclosed in US. Pat. No. 3,176,719. The four-way air valve disclosed therein provides an exhaust passage which is free from obstructions and which permits exhaust air to escape with a reduced tendency to form ice.

One problem associated with the prior art air motor control systems utilizing the four-way air valve is that of excessive noise generated by the exhaust of air. Also while the four-way air valve is effective to prevent formation of ice under most conditions, instances have occurred where under prolonged high-speed operation ice does accumulate and adversely effect the operation of the air motor, particularly when the exhaust air is passed through a muffler, ice then tending to form in the muffler.

Another problem deriving from prior art air motors is that of an uneven or variable power output from the pump. This derives in part from an excessive dwell for the air motor piston while the valve or valves are reversing phase preparatory to driving the piston in the opposite direction. This results in a somewhat sawtooth-type output for the paint being pumped which while partly compensated for by a flexible resilient hose of sufficient length, is undesirable and can prevent optimum results in many instances.

The device of the present invention reduces the difficulties indicated above and affords other features and advantages heretofore not obtainable.

SUMMARY or THE INVENTION It is among the objects of the invention to muffle the noise deriving from the exhaust of air from a double-acting air motor.

Another object is to prevent the formation of ice in a manner harmful to normal operation, during exhaust of air from a double-acting air motor.

Still another object is to provide for the quick reversal of the ports and passages in the control system for operating the piston of a single cylinder, double-acting air motor.

A further object is to provide a control system for a single cylinder, double-acting air motor that will be responsive to a minimum signal and will move with rapid acceleration from one condition to another in response to a modest force and motion.

A still further object is to provide such a control system with a positive reversal which shall be substantially free of any tendency to stall in a dead-center position.

Finally it is an object of the invention to provide such a control system in simple efficient form free from the need of adjustments, easily maintained, easily repaired and assembled in the field, rugged in construction and economical to make and maintain.

These and other objects and advantages are accomplished by means of an apparatus for driving a piston with a compressible fluid through reciprocating travel in a single cylinder double-acting air motor wherein the apparatus includes a fluid pressure supply means and two operating valves for transmitting fluid alternately to opposite ends of the cylinder to drive the piston, and for exhausting fluid alternately in opposite phase from opposite ends of the cylinder. Pilot pressure signals are transmitted alternatingly to each of the operating valves in response to movement of the air motor to control the position of the operating valves. With this arrangement pilot pressure signals move the operating valves simultaneously, but to opposite positions to altematingly supply and exhaust fluid to and from the cylinder.

According to one aspect of the invention the operating valves are provided with a muffler for receiving fluid exhausted from the cylinder through the operating valves. The muffler comprises an open-sided muffler box defining a chamber communicating with the exhaust ports of the operating valves. The open side is covered by a flat flexible closure plate secured to the body portion with marginal portions thereof spaced slightly outward from top edges of the sidewalls of the box to define narrow spaces. When fluid is exhausted through the muffler, the plate may flex outwardly from the box due to fluid pressure so that any ice which may tend to accumulate in the narrow spaces will increase the pressure and be blown out with additional flexing of the plate.

According to another aspect of the invention the muffler is thermally insulated from the operating valves by a thermal barrier means so that the valves will not lose heat to the muffler which is chilled due to the expansion of air as it exits the exhaust ports. With this arrangement the possibility that the valves may be chilled sufiiciently to cause ice to form therein from moisture laden air is substantially reduced.

According to still another aspect of the invention the pilot pressure signals are controlled by a pilot valve operable by the air motor piston. The valve comprises a valve head movable between a pressure signal transmitting limit position and a closed limit position. A resilient overcenter snap action means is operatively connected to the valve head to bias the valve head to each of its limit positions when in the respective limit position. A second resilient means is interposed between the resilient overcenter means and the air motor piston. The second means is flexed during the terminal portion of each piston stroke to generate a force opposed to and greater than the biasing force of the resilient overcenter means to force the resilient overcenter means overcenter whereby the valve head snaps abruptly from one limit position to the other.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation of a double-acting liquid pump and associated single cylinder, double-acting air motor embodying the invention;

FIG. 2 is a front elevation of the pump and air motor of FIG.

FIGS. 3a and 3b are a broken cross-sectional view of the pump and air motor of FIGS. 1 and 2, drawn to an enlarged scale and taken on the line 3-3 of FIG. 1;

FIG. 4 is a fragmentary sectional view taken on the line 4- 4 of FIG. 3b;

FIG. 5 is a cross-sectional view taken on the line 5-5 of FIG. 3B;

FIG. 6 is a cross-sectional view taken on the line 6-6 of FIG. 3b;

FIG. 7 is a sectional view taken on the line 7-7 of FIG. 3a;

FIG. 8 is a cross-sectional view taken on the line 8-8 of FIG. 3a;

FIG. 9 is a fragmentary cross-sectional view taken on the line 9-9 of FIG. 3a;

FIG. 10 is a fragmentary sectional view on a larger scale showing the pilot valve arrangement for the air motor and taken on the line 3-3 of FIG. 1;

FIG. 11 is a fragmentary sectional view taken on the line 11-11 ofFlG.10;

FIG. 12 is a cross-sectional view taken on the line 12-12 of FIG. 3a;

FIG. 13 is a fragmentary sectional view taken on the line 13-13 ofFIG. 3a;

FIG. 14 is a cross-sectional view taken on the line 14-14 of FIG. 3a;

FIG. 15 is a cross-sectional view taken on the line 15-15 of FIG. 3a;

FIG. 16 is a cross-sectional view taken on the line 16-16 of FIG. 3a;

. FIG. 17 is a schematic diagram of the pneumatic control system for the air motor showing the piston in its extension stroke; and

FIG. 18 is a schematic diagram of the pneumatic control system, similar to FIG. 17 but showing the piston in its retraction stroke.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring more particularly to the drawings and initially to FIGS. 1 and 2 there is shown a paint spraying apparatus for use in spraying liquid paint according to the so-called airless method described above in the Background of the Invention." The apparatus comprises a double-acting hydraulic pump A, driven by a double-acting air motor B, and adapted to pump paint from a paint pail C (shown in phantom lines) to a spray gun D (also shown in phantom lines).

Paint from the paint pail C which may be, for example, a standard size drum, enters the hydraulic pump A through an inlet fitting 10 located at the bottom thereof and exits through an outlet fitting 11. From the outlet fitting 11 the paint is directed to-another fitting 12 on a paint filter 13 mounted on the pump A. The paint filter 13 serves to filter out solid particles within the paint that may be too large to pass through the nozzle of the spray gun D.

The paint from the filter l3 exits through an outlet fitting 14 to a flexible hose 15 which extends to the spray gun D. The hose 15 is preferably 25 feet or longer in order to provide some dampening effect in case of variable pressure output from the double-acting pump A. The hose 15 being resilient and flexible, absorbs some energy at the peak pressure periods and thus gives a smoother more uniform pressure output to the spray gun D. The hydraulic pump A cycles at a rate typically about 40 cycles per minute and in a typical instance would have about a 64-cubic inch displacement.

Located at the upper end of the pump A is a solvent chamber 16 and an associated filler cup 17. The chamber 16 maintains a bath of paint solvent around the upper end of the pump piston 18 to dissolve any paint which may accumulate thereon and which when dry could seriously damage the packing through which the upper end of the pump piston 18 slides during its pumping travel.

Air pressure for operating the air motor B is supplied by an air pump 20 through a pressure line 21 which is connected to a pressure regulator valve 22 secured to the air motor B. Air is exhausted from the air motor B through a muffler 23 which serves to muffle the noise of the escaping air and which will be described in greater detail below. A pressure gauge 24 is located at the top of the air motor B (FIG. 2).

AIR MOTOR AND OPERATING VALVES The double-acting air motor B best shown in FIG. 3a comprises an air cylinder 30 mounted between an upper cylinder head 31 and a lower cylinder head 32. The cylinder 30 and the heads 31 and 32 are preferably formed of cast aluminum with the interior surface of the cylinder hard anodized to accommodate frictional loads and to minimize wear. Within the cylinder 30 is a piston 33 mounted on a tubular piston rod 34.

Operating air enters the cylinder chamber and is exhausted therefrom in opposite phase through inlet-exhaust passages 35 and 36 located in the upper cylinder head 31 and lower cylinder head 32 respectively. The control of the inlet and exhaust of air from the respective ends of the cylinder chamber is accomplished by upper and lower poppet-type operating valves 37 and 38 respectively (FIG. 3a).

The valves 37 and 38 are located in an operating valve housing or block40 bolted at one end to the upper cylinder head 3] and at the other end to the lower cylinder head 32. The block 40 has a central air supply passage 41 extending therethrough, which receives operating air from the pressure regulator valve 22 through an inlet fitting 42.

The valves 37 and 38 are poppet-type valves essentially identical to one another and will be described and illustrated using the same numerals for corresponding parts. Each of the valves 37 and 38 is pilot operated, and has a control head 43 and an operating head 44 interconnected by a bolt 45 which serves as a valve stem. The heads 43 and 44 are spaced from one another on the bolt 45 by a perforated spacer sleeve 46 which is radially spaced from the bolt 45 and which extends transversely through the operating air pressure supply passage 41 with operating air being passed around the sleeve 46 or through the perforations in the sleeve 46.

The control head 43 moves or travels between limit positions within a control head chamber 47 defined by a recess in the valve block 40 and by a mating recess in an end block 48 bolted to the valve block 40 with a sealing gasket interposed therebetween. The operating head 44 travels axially between inlet and exhaust positions in an operating head chamber 49 defined by a recess in the valve block 40 and by a cover plate 50 which has exhaust ports 51 through which air may be exhausted from the cylinder through the valves 37 and 38 to the muffler 23 when the respective valve 37 or 38 is in its exhaust position (See valve 38 in FIG. 3a).

The valves control the inlet and exhaust of air to the cylinders through inlet exhaust passages 52 and 53 respectively formed in the valve block 40 and which communicate between the operating head chambers 49 and the inlet-exhaust passages 35 and 36 respectively in the upper cylinder head 31 and lower cylinder head 32.

The position of the operating valve 37 is controlled by a pilot valve 54 which transmits a pressure signal to the chamber 47 of the respective control head 43 through a pilot air passage 55 in the valve block 40 and a mating pilot valve passage 56 in the upper cylinder head 31. In like manner the position of the operating valve 38 is controlled by a pilot relay valve 57 which transmits a pressure signal to the chamber 47 of the respective control head 43 through a pilot relay air passage 58 in the valve block 40 and a mating pilot relay air passage 59 in the upper cylinder head 31.

While the pressures used to transmit pressure signals to the operating valves 37 and 38, and the pressure in the operating air supply passage 41 for operating the piston 33 are essentially the same, the operating force derives from the area differential between the outward face of the control head 43 and its inward face. The effective area against which air pressure acts on the inner face is reduced by the valve stem so that equal fluid pressures on opposite sides of the control head will result in greater force in the direction tending to move the valve to the left as viewed in FIG. 3a. Accordingly when pressure is supplied to a control head chamber 47 at the outward side of the respective control head 43, the respective operating head 44 will bemoved to a position sealing the respective exhaust port 51 while permitting operating air pressure to be transmitted through the perforations in the spacer sleeve 46, into the operating head chamber 49 and out through the respective inlet-exhaust passage 52 or 53 in the valve block 48.

When the pilot pressure signal to a control head chamber 47 at the outward side of the respective control head 43 is cut off however, operating air pressure from the main air supply passage 41 will quickly pop the respective control head 43 and operating head 44 to the right as viewed in FIG. 3a where the operating head 44 will seal the chamber 49 from the main air supply passage 41 while at the same time opening the respective exhaust port 51 so that air may be exhausted to the muffler 23 from the inlet-exhaust passage 52 or 53 respectively through the operating head chamber 49.

Accordingly, the operating heads 44 seat in two sealing positions, one of which is against the cover plate 50 for the valve block 40 to seal the exhaust port 51 and the other of which is against the inner wall of the chamber 49 formed by the valve block 40 to seal the chamber from the main air supply passage 41.

As will be more clearly described below, the pilot valve and pilot relay valve pressure signals are transmitted in opposite phase to the valves 37 and 38 respectively so that correspondingly the positions of the operating heads 44 will be in reverse phase with one another and accordingly operating pressure will be supplied to one end of the cylinder chamber while being exhausted from the other end and vice versa during the operation of the air motor 13.

PILOT AND PILOT RELAY VALVES As indicated above, the air pressure signals for operating the two operating valves 37 and 38 in reverse phase are transmitted by a pilot valve 54 and a pilot relay valve 57. The valves 54 and 57 are best illustrated in FIGS. to 16. Both the valves 54 and 57 are housed in a pilot valve block 65 which is bolted to the top face of the upper cylinder head 31 with a sealing gasket interposed therebetween. The pilot valve 54 is operated mechanically in response to movement of the piston 33 and it comprises an operating head 66 and a valve guide 67 both of which are received on a threaded valve stem 68 and spaced from one another by a spacer sleeve 69. The valve stem 68 extends downwardly into the interior of the tubular piston rod 34 and has a plunger 70 slidably received within the piston rod 34 near the lower end of the cylinder chamber.

On opposite sides of the plunger 70 are coil springs 71 and 72 respectively, the coil spring 71 being located and adapted to be compressed between the plunger 70 and a radial flange of the piston 33 adjacent the upper end of the tubular piston rod 34. Accordingly, energy is stored by the spring 71 during the terminal portion of the piston s retraction travel.

The coil spring 72 is located and adapted to be compressed between the plunger 78 and the bottom of the axial passage within the tubular piston rod 34 during the terminal portion of the extension travel of the piston 33. The stored energy is used to overcome detent force biasing the valve 54 at the valve guide 67 to one or the other of the two detent positions.

The pilot valve 54 is biased to its two detent positions by an overcenter resilient detent means which acts on the valve guide 67 which in turn travels in a valve guide passage 73 defined by the pilot valve block 65 and by a recess 74 in the upper cylinder head 31 through which the valve stem 68 extends.

The resilient overcenter detent means is in the form of two opposed leaf springs 75 and 76 respectively which are mounted in an elastically buckled or flexed condition in slots 77 and 78 in the upper cylinder head 31 (FIGS. 11 and 12). The springs 75 and 76 bear between the ends of the slots 77 and 78 and lateral grooves formed in the valve guide 67. The springs 75 and 76 are so arranged as to exert a maximum detent force in an axial direction against the valve guide 67 when the valve is in either one of its detent positions.

When moving from one detent position to the other the springs 75 and 76 move through an overcenter position where the axial force applied diminishes to zero. Accordingly, energy will be stored in the coil springs 71 and 72 during the terminal portion of piston extension or retraction travel until sufficient force is available to overcome the axial force of the leaf springs 75 and 76 as well asthe force of coulomb friction resisting valve movement. When this force level in the coil springs 71 and 72 is reached the valve 54 begins to move and the motion starts to reduce the axial detent force exerted by the leaf springs. Accordingly, the force exerted by the leaf springs 75 and 76 is progressively reduced and the valve very quickly and abruptly snaps from one detent position to the other.

The pilot valve-operating head 66 travels in a chamber 80 defined by the pilot valve block 65 and a pilot valve cover plate 81 (FIGS. 10 and 16) which is bolted to the block 65 with a sealing gasket 82 interposed therebetween. The chamber 80 has an axial exhaust port 83 defined by the plate 81.

The operating head 66 is movable between two sealing positions in one of which it seals the exhaust port 83 and in the other of which it seals an inlet port 84 in the opposite end of the chamber through which main supply pressure air may be admitted when the port 84 is open. The position of both the operating head and the valve guide 67 relative to the valve stem 68 may be adjusted by an outer spacer sleeve 85 located between adjusting nuts 86 and the outer face of the pilot valve operating head 66. The end of the valve stem 68 and the spacer sleeve 85 extend through the exhaust port 83 and are accessible from the outside to facilitate adjustment.

When the operating head 66 is in its open position a pressure signal is transmitted to the control head chamber 47 of the upper operating valve 37 to open the valve 37 and transmit air pressure to the upper end of the cylinder chamber. Also a pressure signal is simultaneously transmitted to the pilot relay valve 57.

The pilot relay valve 57 comprises a control head 90 and an operating head 91 connected to one another by a bolt or valve stem 92 and spaced apart by a spacer sleeve 93 which fits around the stem 92. The control head 90 moves between two positions in a control head chamber 94 defined by a porting sleeve 95 received in the pilot valve block 65 and by the cover plate 81. An exhaust port 96 extends through the porting sleeve 95 and the block 65 to permit air to be exhausted when the valve is in the position shown in FIG. 10.

The pilot relay valve-operating head 91 travels in an operating head chamber 97 defined by the pilot valve block 65 and the lower end of the porting sleeve 95. The chamber 97 has a pressure inlet port 98 at its lower end which is sealed when the operating head 91 is in one position, and the porting sleeve 95 defines an exhaust port 99 at the upper end of the chamber 97 which is sealed when the operating head is in its other position. Referring to FIG. 14 it will be seen that the pilot relay valve 57 will be in its open position, in other words, opening the inlet port 98 whenever the pilot valve 54 is in its closed position closing its inlet port 84. Accordingly, the pilot relay valve 57 transmits a pressure signal in opposite phase with the pressure signal from the pilot valve 54.

Operating pressure is supplied to the valves 54 and 57 through a passage 186 in the pilot valve block 65, the passage 100 being in communication with the main supply air passage 60 in the upper cylinder head 31. A pilot pressure signal is transmitted to the control head chamber 47 of the operating valve 37 from the pilot valve 54 through a passage 101 in the pilot valve block 65, the passage 101 being in registration with the pilot valve passage 56 in the upper cylinder head 31. The pilot relay valve 57 transmits its pressure signal to the control head chamber 47 of the operating valve 38 through still another passage 102 in the pilot valve block 65, the passage 102 being in registration with the pilot relay valve passage 59 in the upper cylinder head 31. The pressure signal from the pilot valve 54 to the control head chamber 94 of the pilot relay valve 57 is transmitted through a passage 103 which is in communication with the pilot valve passage 101.

MUFFLER According to one aspect of the invention a unique muffler 23 is provided for reducing the noise caused by the rapid exhaust of pressurized air from the cylinder chamber through the operating valves 37 and 38. The unique construction of the muffler 23 minimizes the problem of ice formation which is often encountered due to.the rapid expansion of moisture laden air as it is exhausted.

The muffler 23 comprises a muffler box 110 bolted to the operating valve block 40. The box 110 has a floor with exhaust ports 111 formed therein that register with the exhaust ports 51 in the cover plate 50, and an open top face which is covered by a cover plate 112 to define within the box a muffler chamber 113. The cover plate 112 is formed of relatively thin, flexible material and may have longitudinal reinforcing ribs 114. This construction permits the plate 112 to flex or bend in a lateral plane.

The cover plate 112 is secured to the box 110 in a manner to permit such resilient flexing by means of three spaced bolts 1 which extend through the cover at spaced locations along a central longitudinal line and which are received in posts 116 extending upwardly from the floor of the muffler box 110. With this arrangement the plate 112 may flex or bend outwardly slightly in response to pressure within the' mufiler chamber 1 13.

The sides of the top plate 1 12 are spaced from the adjacent edges of the sidewalls of the muffler box 110 to define narrow exhaust spaces 117, approximately 0.015 inch wide through which exhaust air may escape from the muffler chamber 113 While ice may form in the narrow spaces 117 due to the high velocity and rapid expansion of moisture laden air escaping therethrough, such formation will increase the pressure within the chamber which in turn will cause the plate 1 12 to flex outwardly. This flexing will cause blowout or purging of the ice from the spaces and thus prevent ice accumulation.

The muffler box 110 is thermally insulated from the valve block 40 by a thermal barrier comprising both an insulating gasket 118 preferably formed of a dielectric material, and an air space 1 19. Air is free to circulate through the space 119 so that the operating parts of the valves 37 and 38 will be maintained advantageously at a relatively warm temperature and will not be chilled by the muffler box which is cooled by the rapid expansion of the air being exhausted therethrough.

PUMP

The construction of the pump A is best illustrated in FIGS 3b through 6 and it includes the solvent chamber 16 as well as the pumping cylinder itself. The solvent chamber 16 is formed in part by the lower cylinder head 32 of the air motor B and by a matching solvent chamber block 120. The block 120 and the lower cylinder head 32 have a sliding fit with one another and are held in axial position by flange bolts or tie rods 121 which extend up to the upper cylinder head 31 and serve to secure the air cylinder assembly and block 120 together.

A solvent enters the solvent chamber 16 through the filler cup 17 and is most advantageously maintained near the top of the filler. The solvent serves to dissolve any paint which may collect on the surface of the piston 18 and which could dry thereon and by abrasive action seriously damage'the packings through which the piston 18 slides.

The pumping action is accomplished within a cylindrical housing including an upper pump cylinder 122 and lower pump cylinder 123. The upper end of the upper pump cylinder 122 is secured to the solvent chamber block in a circular recess 127 in the bottom thereof by a retainer plate 124. The upper pump cylinder 122 has a pair of radially extending ears 125 adjacent its upper end and the retainer plate 124 has a central opening 126 contoured to receive the upper end of the upper pump cylinder 122 and the ears 125 when in one condition. However the upper pump cylinder 122 when inserted is rotated 90 so that the ears are tightly seated and retained by the retainer plate 124 in the recess 127 (FIG. 4).

Located within the upper pump cylinder 122 is an upper packing sleeve 128 which seals and guides the piston 18 by means of a packing gland 129 carried therein. Another packing sleeve 130 is mounted in the lower end of the upper pump cylinder 122, the sleeve 130 also having a packing gland 131.

The spacing between the packing sleeves 128 and 130 must be very accurately fixed and maintained within very narrow dimensional tolerances. A solid spacer sleeve would therefore require extremely accurate dimensioning and would not accommodate dimensional variations in other parts such as the packing sleeves themselves.

The pump of the present invention however has a resilient expanded metal spacer sleeve 132 which maintains proper spacing between the packing sleeves 128 and 130 while at the same time being resilient enough to accommodate some dimensional variations in other parts. The sleeve 132 is formed of expanded metal which after being expanded according to practices well known in the art is rolled into a flat sheet form. The rolled sheet is then cut to size and formed into a cylinder which may or may not have its lateral surface abutted Accordingly, the spacer sleeve 132 can be compressed while still exerting sufficient force to maintain the packing sleeves 128 and 130 in spaced apart relation and prevent axial movement thereof as the piston 18 slides therethrough. While a round wire coil spring could serve the same purpose, it would require excessive space to provide the same force and rate and thus would be undesirable.

The lower pump cylinder 123 is secured within the upper pump cylinder 122 in the manner shown in FIG. 3b with its upper end resting against the bottom of the lower packing sleeve 130.

The piston 18 has an upper end 134 of smaller diameter which travels entirely within the upper pump cylinder 122 and the solvent chamber 16, and also a tubular lower end 135 of enlarged diameter with an axial passage 136 located therein. The upper end 134 of the piston is connected to the lower end of the piston rod 34 of the air cylinder at a threaded connection indicated at 137 in FIG. 3a.

The upper pump cylinder 122 and lower pump cylinder 123 define an outlet chamber 138 and an inlet chamber 139 respectively, the passage 136 within the lower end 135 of the piston 18 being in communication with the outlet chamber 138 through ports 140 at the upper end thereof. A ball check 141 is located at the inlet fitting 10 to the pump inlet chamber 139 and a second ball check 142 is located in the passage 136 at the lower end 135 of the piston 18.

Considering reciprocating movement of the piston 18 beginning with the piston extended downwardly to the lower end of the pump housing, the beginning of the upward retraction movement will open the ball check 141 and close the ball check 142 and liquid paint will be drawn into the pump inlet chamber 139. This continues until the piston 18 reaches its retracted or raised position shown in FIG. 3b.

During the same upward retraction movement, liquid paint located in the pump outlet chamber 138 will be forced out through the outlet fitting 1 1. The volume pumped out through the outlet fitting 11 during this movement is one-half the volume drawn into the inlet chamber 139.

During the downward extension movement of the piston 13 the ball check 141 will close and the ball check 142 will open so that paint in the pump inlet chamber 139 will be forced through the axial passage 136 in the lower end 135 of the piston 18 and into the outlet chamber 138.

Since essentially all of the liquid paint in the inlet chamber 139 will be displaced during the downward extension movement and since only one-half the volume of the inlet chamber 139 is displaced out the port, the other half remaining in the chamber 133, one-half of the volume paint which is pumped out of the inlet chamber 139 will also be pumped out of the outlet chamber 133 through the outlet fitting 11.

Accordingly an equal volume of paint is pumped during both extension and retraction movement of the piston 13 so that a generally uniform output of liquid paint is supplied to the spray gun D, the only interruption in pressure output occurring at the instant that the piston 18 reverses its travel.

The transient variation in output occurring at the instant of piston travel reversal however, is dampened out in the supply hose 13 from the filter 113 to the spray gun D, which is generally 25 feet or longer to provide a dampening effect due to the resilient character of the hose.

AIR MOTOR OPERATION The control and operation of the air motor B is best illustrated and described with reference to FIGS. 17 and 18 which present schematically the two conditions of the operating valves 37 and 33, the pilot valve 54 and the the pilot relay valve 57. Figure 17 shows the piston 33 about midway through its downward retraction travel and it will be seen that the pilot valve 54 is in its upward position with the valve guide 67 being urged to the corresponding detent position by the overcenter leaf springs 73 and 76. The pilot valve 54 in this position transmits a pressure'signal to the control head 43 of the upper operating valve 37 and another simultaneous and correspond ing pressure signal to the control head 90 of the pilot relay valve 57. Accordingly, the operating head 91 of the pilot relay valve 57 is moved to the closed position to cutoff pilot pressure to the control head 43 of the lower operating valve 38.

Thus, the control head 43 of the upper operating valve 37 moves the respective operating head 44 to the pressure inlet position so that air pressure is supplied to the upper end of the air motor cylinder chamber. Since the pilot relay valve 57 is moved to its closed position, no pilot pressure signal is transmitted and air in the chamber 97 is vented. Accordingly, the control head 43 of the lower operating valve 38 and the operating head 4M1 thereof are moved to the exhaust position so that air is exhausted from the lower end of the air motor cylinder chamber. It will be seen that operating air pressure acting on the inward side of the control head 43 of the lower operating valve 33 forces the operating head positively into its exhaust position, the force being derived from the pressure differential since there is no positive pressure acting on the outward side of the control head 43.

As the piston 33 reaches the terminal part of its downward retraction movement the coil spring 71 begins to be compressed between the plunger 70 and the upper end of the piston rod 34. Accordingly, energy is stored in the coil spring 71 to provide a progressively increasing force until the force is sufficient to overcome the resisting force of the overcenter leaf springs 75 and 7s as well as coulomb friction. As this occurs, the valve guide 67 moves downwardly and as described more specifically above, very abruptly moves past its overcenter position into its opposite or downward detent position wherein the leaf springs exert a biasing force in the downward direction.

The condition of the system at this time is best illustrated diagrammatically in FIG. 18. The pilot valve 543 having been moved to its downward detent position, the pressure signal to the control head 13 of the upper operating cylinder 37 is cut off and vented as well as the pressure signal to the pilot relay valve 57. Thus, the pilot relay valve 57 is suddenly and abruptly forced by operating air pressure acting against the in- 111i side face of the control head to the open position thus transmitting a pressure signal to the control head 13 of the lower operating valve 38.

Accordingly, the operating head M of the upper operating valve 37 is moved to its exhaust position so that air is exhausted from the upper end of the cylinder chamber while the operating head of the lower operating valve 38 is moved to its pressure transmitting position and operating pressure is supplied through the valve 38 to the lower end of the air motor cylinder chamber. The resulting pressure moves the piston 33 through its upward extension stroke travel to a point where near the terminal portion of its extension travel the coil spring 72 begins to be compressed between the plunger 71) and the floor of the passage in the piston rod 34 until sufficient energy is stored to supply a force to overcome the overcenter leaf springs 75 and 76. As this occurs the pilot valve 541 abruptly snaps to its opposite position to transmit pilot pressure signals to the upper operating valve 37 and the pilot relay valve 57 so that the valve condition changes to that discussed above with respect to FIG. 17.

While the invention has been shown and described with reference to a specific embodiment thereof this is for the purpose of illustration rather than limitation and other modifications and variations will be apparent to those skilled in the art upon reading of the specification, all with the intended spirit and scope of the invention. Accordingly the patent is not to be limited to the form specifically illustrated and described nor in any manner that is inconsistent with the extent to which the progress in the art has been advanced by the invention.

We claim:

1. Apparatus for controlling the transmission of fluid pressure to a double-acting fluid motor cylinder for driving a reciprocating piston therein, comprising fluid pressure supply means, two pilot pressure responsive operating valves for transmitting fluid pressure from said pressure supply means altematingly to opposite ends of said cylinder and for exhausting fluid altematingly from opposite ends of said cylinder, pressure responsive first means for transmitting a pilot pressure signal to one of said operating valves, second means operable by said piston for transmitting a pilot pressure signal to the other of said operating valves and for simultaneously transmitting a pilot pressure signal to said first means whereby said first and second means move said operating valves alternatingly to opposite positions.

2. Apparatus as defined in claim 1 including a mufiler for receiving fluid exhausted from said cylinder through said operating valves.

3. Apparatus as defined in claim 1 wherein said first means and said second means comprise three-way poppet valves operatively associated with said fluid pressure supply means.

4. Apparatus as defined in claim 3 'wherein the three-way poppet valve of said second means is provided with a resilient, overcenter snap action means for urging said valve to either of two detent positions.

5. Apparatus as defined in claim 4 wherein said snap action means comprises diametrically oppose-d leaf springs buckled to exert opposed radial forces and movable between opposite overcenter limit positions to exert a biasing force acting on said valve when said valve is in one of its detent positions and a biasing force acting on said valve in the opposite direction when said valve is in the other of its detent positions.

6. Apparatus as defined in claim 1 wherein said operating valves are three-way poppet valves.

7. Apparatus for driving a piston with a compressible fluid through positive reciprocating travel in the cylinder of a double-acting fluid motor comprising fluid pressure supply means, two fluid pressure responsive operating valves for transmitting fluid pressure altematingly to opposite ends of said cylinder and for exhausting fluid altematingly from opposite ends of said cylinder, a fluid pressure responsive pilot relay valve for altematingly transmitting a fluid pressure signal to one of said operating valves to control the position of said one operating valve, a pilot valve operable by said piston to altematingly transmit a fluid pressure signal to said pilot relay valve and to the other of said operating valves to control the position of said other operating valve and said fluid-operated pilot valve, whereby said pilot relay valve moves said one operating valve simultaneously with said other operating valve to an opposite position.

8. Apparatus as defined in claim 7 wherein said pilot valve comprises a valve stem operatively connected to said piston to be moved thereby during the terminal portions of said piston s extension and retraction travel, a valve head carried by said stem and movable between two detent positions, spring means interposed between said stern and said piston whereby said spring means is compressed whenever said valve stem is moved in either direction by said piston, and resilient, overcenter snap action means urging saidhead to either of its detent positions to resist movement thereof in response to compression of said spring means until a balanced force condition is reached whereby upon further spring compression, said valve head snaps to its opposite detent position.

9. Apparatus for driving a piston with a compressible fluid through positive reciprocating travel in the cylinder of a double-acting fluid motor, comprising fluid pressure supply means, two pilot pressure responsive operating valves for transmitting fluid pressure alternatingly to opposite ends of said cylinder and for exhausting fluid alternatingly from opposite ends of said cylinder, a fluid pressure responsive pilot relay valve for alternatingly transmitting a pilot pressure signal to one of said operating valves to control the position of said one operating valve, a pilot valve comprising a valve stem operatively connected to said piston to be moved thereby during the terminal portions of said piston extension and retraction travel, a valve head carried by said stem and movable between two detent positions, spring means interposed between said stem and said piston whereby said spring means is compressed whenever said valve stem is moved in either direction by said piston, and resilient, overcenter snap action means urging said head to either of its detent positions to resist movement thereof in response to compression of said spring means until a balanced force condition is reached suchthat upon further spring compression said valve head snaps to its opposite detent position, whereby said pilot valve transmits a pilot pressure to the other of said operating valves and simultaneously transmits a pilot pressure signal to said pilot relay valve to operate said operating valves alternatingly to opposite positions, an open-sided box defining a muffler chamber communicating with exhaust ports of said operating valves, a flexible closure plate adapted to cover the open side of said box with marginal portions thereof spaced slightly from the top edges of the sidewalls of said box to define narrow exhaust spaces, said plate being mounted to permit flexing thereof to move said marginal portions outwardly from said box in response to pressure in said chamber.

10. Apparatus for controlling the transmission of fluid pressure to a double-acting fluid motor cylinder for driving a reciprocating piston therein comprising fluid pressure supply means, two pilot pressure responsive operating valves for transmitting fluid pressure from said pressure supply means alternatingly to opposite ends of said cylinder and for exhausting fluid alternatingly from opposite ends of said cylinder, and means operable by said piston for transmitting pilot pressure signals alternatingly to said operating valves to control the driving of said piston, said means including a pilot valve operatively associated with said pressure supply means and comprising a valve head movable between two limit positions, first resilient means operatively connected to said valve head and adapted to move between overcenter limit conditions to bias said valve head to each of its limit positions when said valve head is in the respective limit position, and second resilient means operatively connected to said first resilient means and adapted to be flexed alternatingly in opposite directions by said piston to generate a force opposed to and greater than the biasing force of said first resilient means to force said first resilient means abrupty from one condition to the other and to force said valve hea abruptly from one limit position to the other.

11. Apparatus for controlling the transmission of fluid pressure to a double-acting fluid motor cylinder for driving a reciprocating piston therein comprising fluid pressure supply means, two pilot pressure responsive operating valves for transmitting fluid pressure from said pressure supply means alternatingly to opposite ends of said cylinder and for exhausting fluid alternatingly from opposite ends of said cylinder, means operable by said piston for transmitting pilot pressure signals alternatingly to said operating valves to control the driving of said piston, and a mufller for receiving fluid exhausted from-said cylinder through said operating valves, said muffler comprising an open sided box defining a chamber communicable with exhaust ports of said operating valves, a flexible closure plate adapted to cover the open side of said box with marginal portions thereof spaced slightly from the top edges of the sidewalls of said box to define narrow exhaust spaces, said plate being mounted on said box to permit flexing of said plate to move said marginal portions outwardly from said box whereby said plate may be flexed by pressure in said chamber to cause removal of ice which may form in said spaces during the exhaust of moisture laden air.

12. Apparatus as defined in claim 11 including thermal insulating means interposed between said operating valves and said box. 

1. Apparatus for controlling the transmission of fluid pressure to a double-acting fluid motor cylinder for driving a reciprocating piston therein, comprisinG fluid pressure supply means, two pilot pressure responsive operating valves for transmitting fluid pressure from said pressure supply means alternatingly to opposite ends of said cylinder and for exhausting fluid alternatingly from opposite ends of said cylinder, pressure responsive first means for transmitting a pilot pressure signal to one of said operating valves, second means operable by said piston for transmitting a pilot pressure signal to the other of said operating valves and for simultaneously transmitting a pilot pressure signal to said first means whereby said first and second means move said operating valves alternatingly to opposite positions.
 2. Apparatus as defined in claim 1 including a muffler for receiving fluid exhausted from said cylinder through said operating valves.
 3. Apparatus as defined in claim 1 wherein said first means and said second means comprise three-way poppet valves operatively associated with said fluid pressure supply means.
 4. Apparatus as defined in claim 3 wherein the three-way poppet valve of said second means is provided with a resilient, overcenter snap action means for urging said valve to either of two detent positions.
 5. Apparatus as defined in claim 4 wherein said snap action means comprises diametrically opposed leaf springs buckled to exert opposed radial forces and movable between opposite overcenter limit positions to exert a biasing force acting on said valve when said valve is in one of its detent positions and a biasing force acting on said valve in the opposite direction when said valve is in the other of its detent positions.
 6. Apparatus as defined in claim 1 wherein said operating valves are three-way poppet valves.
 7. Apparatus for driving a piston with a compressible fluid through positive reciprocating travel in the cylinder of a double-acting fluid motor comprising fluid pressure supply means, two fluid pressure responsive operating valves for transmitting fluid pressure alternatingly to opposite ends of said cylinder and for exhausting fluid alternatingly from opposite ends of said cylinder, a fluid pressure responsive pilot relay valve for alternatingly transmitting a fluid pressure signal to one of said operating valves to control the position of said one operating valve, a pilot valve operable by said piston to alternatingly transmit a fluid pressure signal to said pilot relay valve and to the other of said operating valves to control the position of said other operating valve and said fluid-operated pilot valve, whereby said pilot relay valve moves said one operating valve simultaneously with said other operating valve to an opposite position.
 8. Apparatus as defined in claim 7 wherein said pilot valve comprises a valve stem operatively connected to said piston to be moved thereby during the terminal portions of said piston''s extension and retraction travel, a valve head carried by said stem and movable between two detent positions, spring means interposed between said stem and said piston whereby said spring means is compressed whenever said valve stem is moved in either direction by said piston, and resilient, overcenter snap action means urging said head to either of its detent positions to resist movement thereof in response to compression of said spring means until a balanced force condition is reached whereby upon further spring compression, said valve head snaps to its opposite detent position.
 9. Apparatus for driving a piston with a compressible fluid through positive reciprocating travel in the cylinder of a double-acting fluid motor, comprising fluid pressure supply means, two pilot pressure responsive operating valves for transmitting fluid pressure alternatingly to opposite ends of said cylinder and for exhausting fluid alternatingly from opposite ends of said cylinder, a fluid pressure responsive pilot relay valve for alternatingly transmitting a pilot pressure signal to one of said operating valves to control the position of said one operating valve, a piloT valve comprising a valve stem operatively connected to said piston to be moved thereby during the terminal portions of said piston''s extension and retraction travel, a valve head carried by said stem and movable between two detent positions, spring means interposed between said stem and said piston whereby said spring means is compressed whenever said valve stem is moved in either direction by said piston, and resilient, overcenter snap action means urging said head to either of its detent positions to resist movement thereof in response to compression of said spring means until a balanced force condition is reached such that upon further spring compression said valve head snaps to its opposite detent position, whereby said pilot valve transmits a pilot pressure to the other of said operating valves and simultaneously transmits a pilot pressure signal to said pilot relay valve to operate said operating valves alternatingly to opposite positions, an open-sided box defining a muffler chamber communicating with exhaust ports of said operating valves, a flexible closure plate adapted to cover the open side of said box with marginal portions thereof spaced slightly from the top edges of the sidewalls of said box to define narrow exhaust spaces, said plate being mounted to permit flexing thereof to move said marginal portions outwardly from said box in response to pressure in said chamber.
 10. Apparatus for controlling the transmission of fluid pressure to a double-acting fluid motor cylinder for driving a reciprocating piston therein comprising fluid pressure supply means, two pilot pressure responsive operating valves for transmitting fluid pressure from said pressure supply means alternatingly to opposite ends of said cylinder and for exhausting fluid alternatingly from opposite ends of said cylinder, and means operable by said piston for transmitting pilot pressure signals alternatingly to said operating valves to control the driving of said piston, said means including a pilot valve operatively associated with said pressure supply means and comprising a valve head movable between two limit positions, first resilient means operatively connected to said valve head and adapted to move between overcenter limit conditions to bias said valve head to each of its limit positions when said valve head is in the respective limit position, and second resilient means operatively connected to said first resilient means and adapted to be flexed alternatingly in opposite directions by said piston to generate a force opposed to and greater than the biasing force of said first resilient means to force said first resilient means abruptly from one condition to the other and to force said valve head abruptly from one limit position to the other.
 11. Apparatus for controlling the transmission of fluid pressure to a double-acting fluid motor cylinder for driving a reciprocating piston therein comprising fluid pressure supply means, two pilot pressure responsive operating valves for transmitting fluid pressure from said pressure supply means alternatingly to opposite ends of said cylinder and for exhausting fluid alternatingly from opposite ends of said cylinder, means operable by said piston for transmitting pilot pressure signals alternatingly to said operating valves to control the driving of said piston, and a muffler for receiving fluid exhausted from said cylinder through said operating valves, said muffler comprising an open sided box defining a chamber communicable with exhaust ports of said operating valves, a flexible closure plate adapted to cover the open side of said box with marginal portions thereof spaced slightly from the top edges of the sidewalls of said box to define narrow exhaust spaces, said plate being mounted on said box to permit flexing of said plate to move said marginal portions outwardly from said box whereby said plate may be flexed by pressure in said chamber to cause removal of ice which may form in said spaces during the exhaust of moisture laden air.
 12. Apparatus as defined in claim 11 including thermal insulating means interposed between said operating valves and said box. 